It could be a number of different things.

Take her to a GP. If you cant get in to see a doctor, take her to the chemsit and get an opinion from the pharmacist.

DS gets something simlar. his is eczema - but it doesnt stay around like you are describing, it comes and goes, and especially when he eats certain foods.

Dont stress about the teethers having been in the freeezer, you can only do the best with the information you are given. It doesnt mean that thats what has happened.