3 year old ADHD - parents are at wits end.

Relentless 3 year old never stops talking… when others are trying to talk she just starts saying random shit louder and louder until the people talking are having to raise their voices just to talk. You tell her to stop, she does for 2 seconds, then literally starts again. She is on the go ALL DAY EVERY DAY with what seems like an endless amount of energy. I’ve told her doctor that she has ADHD, but they don’t diagnose until school age. Which I don’t understand why because she clearly has ADHD (dad has adhd and mom has AUDHD Ive asked if there’s respite care for kids w adhd parents….. no…. Her dad is a stay at home dad because he’s on disability. I work full time and once I get home, I try to relieve dad from the relentless demand of this kid! We can’t afford day care and don’t qualify for financial assisted daycare because “both parents have to work outside the home for 30 hrs per parent” I take her to my moms a day/night a week or 2 weeks but my mom also has my brother and his 4 children there and they are a bit demanding too. My mom has even said my child is A LOT. Even compared to my brothers 4 (which is saying a lot because they have odd and adhd too)

Dad is about to have a heart attack(anxiety/mental break down) because he never really gets a break.

Anyone out there w advise or help?