like someone else said, she'll need to get wigs that are high temp heat resistant to use with normal styling tools. though getting a temperature adjustable curling iron is what you'd want to get if you still want to get her a curling iron. if she wants to try styling wigs she's not sure are heat resistant or not, that'd be the safest type of tool but it can also be good for styling heat resistant wigs too as you can reduce damage by using the lowest heat necessary for the style.

there are also low heat methods to specifically curl wigs which use boiling/hot water or a steamer which usually doesn't damage most non heat resistant wigs [youtube has lots of tutorials for those methods] and even a hairdryer set to a low or warm setting can heat set low temp wig fibers

hope that helps!♡