3 yo waking up at night

So my 3 yo used to sleep thru the night since I can remember .. bedtime is 7pm (she’s dropped naps) and she’d be up in the morning 6:30-7:30... For the past cpl wks she’s been walking up at 11pm /12am/ 3/4am coming out of her room turning all the lights on and going to her sisters room waking her up 😢 She keeps saying it’s morning and I can’t get her to go back to bed I’ve tried taking her in my bed.. she won’t go back to sleep till the morning only tossing and turning... I called the dr she’s like oh they start dreaming around this age maybe she’s having bad dreams..

I am exhausted but feel worse for my baby being up for so long sometimes I just drive her around she sleeps under 1hr..

Anyone else been thru this? Btw there’s been no changes in diet or anything..

Thank you!