I was trying to find some info, but without a luck, so here I am. Usually I have painted over the nails, added some highlights and it was ok, but here the look doesn't look good at all. The color does't have to be red, could be gold or yellow, but anyway, have no idea how to fix that !

Help!

try a different blend mode, overlay or hard light can give a more glossy look,
of course you'd have to fix chipped peeling parts separately.
I'll have example ready in a few.

this is overlay + highlights

thx for help, but it still doesn't look well. I can see in yours retouch darker red spots from her original nail polish...

Original photo has a lot of noise. Add the same noise into the nails and they'll blend in better.

I was just illustrating a way that it could be done.
It was from very small, noisy original.