I see a roleplay hook!
For those times like you describe where the other players swoop in and drop your target, leaving no one for you to face, play up your character's chill. Have her congratulate the ally, say something like "That saves me the fuss" and take a calm relaxed swig of water as you stroll on to your next target.
Let her be relaxed about not being the one to drop the foes - it doesn't have to bother her because she knows she's skilled. She doesn't have to prove it.
I absolutely love this. Thank you!
Or take them from the fighter who keeps bogarting your targets !
In 3rd edition I had a similar problem. I was playing a barbarian with great cleave. I can't remember if we were using a houserule feat, but I had the ability to cleave then move, cleave then move, cleave then move, ad infinitum, as long as the target went down. The damn druid kept sending his hoard of summoned animals to pick off of the enemies with low hit points. After mentioning several times that his animal hoard kept breaking the links in my cleave chain, the next time it happened I just cleaved through the pack of summoned critters to get to the foe. Only needed to do that once.
Ahahaha, wow! That's one way to make a point.
Keep in mind that there may be nothing malicious here. Some players have a hard enough time figuring out what they are going to do next, much less consider what other players plan on doing or are capable of doing. Next time, roleplay who your next target is going to be. "Yo, lickspittle. You're next." This should help give the other players an idea of your plans without breaking the 4th wall.
This is true -- and is definitely, obviously a problem for at least one of our players. I'm going to try and do better at giving some people grace.
It actually sounds like RP might be causing some of the "issues". Most of the characters I play would be more likely to finish off an enemy in melee with a "very chill middle-aged hippie woman who isn't nearly as bothered by the lack of tactics" than most other PCs even just a change to a "very chill middle-aged hippie woman who makes it obvious that she is taking care of business and doesn't want any help".
Basically, how much do you RP in combat? Do you make things clear to the other players (in character) when you are in over your head or don't want them to focus fire and help you?
Ask the GM why they are placing opponents as far apart as they are, it might just be that they don't really think about it. Consider how your PC would handle the choice, but get yourself some ranged options even if it involves "wasting" spells.
I'm going to kind of get a little tl;dr here again for the sake of answering your questions about both RP and DM enemy placement.
Our DM for this particular game was new to DMing. She chose SKT because it was the only campaign built into Roll20 at the time, and didn't consider what she might enjoy running, or what might be easier for her to run as a newbie DM. When we created characters, we didn't create characters who would necessarily be the best fit for the campaign (none of us knew what the campaign was even about), and we didn't have any hooks that gave us compelling reasons to be drawn into the giant drama. As a result, the party didn't exactly have the best chemistry, and most were lukewarm to the whole giant business at best. Compared to the Thursday game, which is so RP-heavy that several of us actually do one-on-one roleplay sessions in between sessions so it's not taking up the brunt of our regular all-party game sessions, Saturday is RP-lite.
Half the party ended up rolling up new characters, and while there's definitely more chemistry than there was before (and a shared goal -- something that we really didn't have with the original party), but there's not a ton of RP happening outside of combat, and there's not much happening in-combat. The extent of my RP in-combat in the game right now is figuring out how my character would react to certain situations -- and most of the time, that involves following the lead of others, which is (usually) pretty easy, given that I'm a paladin so I'm usually closer to the bottom of the initiative order than I am the top.
Because the DM is new, she usually follows what's written in the module to the letter. I'm just doing research for my first campaign now (I'm reading through Strahd first, then PotA, and then I'll worry about making choices), and I've become acutely aware from just a cursory readthrough that sometimes, things in this book don't make sense, or are going to be extremely difficult / challenging, depending on the party makeup. Even as I read through Strahd, I'm already making a mental note of things that I'll likely have to tweak.
I think it's the lack of confidence/experience that makes it difficult for her to feel comfortable going off the page. There were elements to this particular combat that could have been adjusted to make it not feel so much like a long-lasting, miserable deathmatch with enemies all over the board, but I get the feeling she didn't feel comfortable making them because she thinks the book knows better than she does. (This is just my observation/speculation, though -- I might be totally off-the-mark.)
After taking in all the advice here, I'm definitely going to invest in something ranged. I might not be able to do a lot of damage with it, but at least it'll help to mitigate my frustration at feeling like there's little for me to do in combat... particularly when combat seems to be so much of our game, lately.