Potty train 😭😖

My daughter is 2 and 6 months old at 18 month I started potty train her but she wasn’t ready then at 2 again and wasn’t ready and now I’m trying but she won’t pee or poop she will hold it and when she finally does she holds it in and she pees but only a little, as soon as I put the diaper on her she pees a lot 😒 I’m afraid she will get a UTI because she would not get everything out 😞 this happend to my now 6 yo what should I do? I took her diaper off at 7:30 and just now at 2:30 she peed but only a little in her little toilet and she is drinking a lot of water!!