One question is, is it OK for a player to roleplay their character in such a way that it may bring negative consequences to themselves and the group. And to that I say, absolutely it's OK! In fact, when I have a player roleplay that way, I get excited, because it fits into the kinds of games I want, and that is the kind of player I want - one who is focused on "telling a good story" instead of focused on "I need to win this game." My belief is that roleplaying is primarily a group story-telling activity with game elements thrown in, rather than a game with story-telling elements thrown in. There is a balance there, though, and it's not polite to play a character with so many flaws that they are constantly a hindrance and problem to their teammates. Ashley was neither; she did fine!
I think this is somewhat close to a false dichotomy though. It's very possible to both tell a good story and focus on "winning," assuming that means you're shooting for more success than failure or even mostly success. There are so many ways to portray a character's flaws in an entertaining way that isn't also actively hurting the rest of the party.
But the other question is whether a player can determine the actual crunch and rules to apply to a given situation. And I say, no! That's the DM's job, and it begins to get a bit rude when players are deciding that they are going to make a skill roll just because they should, or deciding they are going to get advantage, because reasons, without at least asking the DM. Usually they shouldn't even ask, unless it's a situation where a roll might need to apply and it's easy for a DM to pass over it. Otherwise, they should focus on the narrative of what they are doing, and let the DM decide if any crunch rules and dice rolls and modifiers should apply. Again, Ashley asked Matt in a courteous way and was respecting his decision one way or another, so she did fine.