Bringing back memories for me. I had a super stubborn 4 year old son. I kind of left her alone. We had a doctors appointment and we talked to the doctor about school. And I said to the doctor that he (my son) does not want to get potty trained. She (the doctor) was like WHAATTTT? You don't want to go to school in a diaper, do you? My son stayed silent. When we got home, I said "hey, would you just get potty trained already?" and he said "okay" with a sort of eye roll. And I kid you not, he was potty trained from that moment on. No accidents like I had with my son before him who potty trained earlier.
Now, some kids have a hard time leaving enough time to get to the bathroom because they are so busy, having fun OR they don't get a strong signal to go until it is too late. Talk to her about any signs that SHE has before she has to go, wiggling, crossing legs, etc. And direct her to the bathroom. You don't have to reward her with anything but praise if she goes.
When does she start school?
Oh, and now I"m reading you are not the custodial parent and only have her 2 weekends so 4 days a month. You are kind of stuck. Have you talked to her mom about it to come up with a consistent plan to be followed at both places, yours and hers? That's the first step.