We finished up the design of my daughter's character and she had a chance to play her in a short adventure (Mission 1 of Harried in Hillsfar). Here are the mechanics we settled on:
-Tremorsense to 100' when barefoot and on earth or stone. (No reason for reduction from 120 other than I remembered wrong when we wrote it up on her sheet)
-Blindsight to 10' (barefoot not a requirement, due to involvement of other senses)
-enemies who are not "grounded" have advantage on attacks/she has disadvantage vs. "ungrounded" enemies.
-A -2 penalty on her AC when defending against ranged attacks from grounded enemies
-Automatic failure of checks dependent on sight; Disadvantage or -2 penalty on checks that are mostly/partially dependent on sight, at DMs discretion.
-We created a homebrew, earth-based ranged attack cantrip, with varying damage and/or effects depending on the type of earth she's in contact with, in place of the crossbow/hand axes on the equipment list. She suggested varying the damage/effects, and let me set up the mechanics for those. (If folks are interested, I can post it, but I won't bore you with it unless you ask.)
The AC penalty allowed us to split the difference between attackers having advantage on ranged attacks and there being no difference at all with a sighted character. Part of the rational is that her tremorsense may allow her to recognize when a ranged weapon is shot at her (although when she played yesterday she was pretty self-limiting as to the detail tremorsense gives her). But between release and her 10 ft blindsight radius, she can't track the arrow/bolt/knife because it's not grounded. 10 ft gives her a bit of time to respond, but not much.
She does have a seeing-eye prairie dog, mostly for flavor. I haven't bothered with mechanics for it.
When we played yesterday, she was very aware of what her character could and couldn't know due to her blindness. (Not surprising, she's a bright teenager and very into narrative/immersive storytelling). I can tell it will push me as a DM to find ways to be clear about some of that as well.
It also means I have to be alert to what the "floor" material is, a detail most adventures don't bother with. So far we haven't had any combat encounters off of earth or stone, although that issue did show up in social interaction/role-playing episode, and I was pleased to see how seriously she took it.
I'm looking forward to the next mission in Harried in Hillsfar, where her tremorsense will make a difference in a basement encounter.
Thanks again for the suggestions. It's also interesting to see different philosophies, and the range from those who (like me) lean more toward mechanics and those who (like my daughter) lean more toward role playing. (not that those are mutually exclusive. Further it's good for me to be stretched to focus more on role-playing and be a bit less obsessive about the rules/mechanics).