Kind of strange she looks thin if she was fed every 4 days... You can definitely stick to that schedule. I fed every 5 days when mine were smaller. I wouldn't start to worry until she hasn't eaten for a month or so, or if she starts losing weight. Do you know if this is her first f/t meal? Hopefully once she has some time to settle in, she'll eat like a champ for ya.
On the wrinkly skin, she's probably going to shed soon. What's her setup like? Hides? Temp and humidity?
Oh yeah, and send pics if you have them!