Should you let your 8 year old daughter wear knickers over tights?

Hi, my daughter is 7yrs old and she does wear knickers over her tights aswell as under. she finds her tights stay up better that way plus if she is playing with friends and her dress rises they can only see her top knickers. she has had one or two friends ask why she wears knickers over her tights but after she explains they just seem to take it as a normal thing (which i think it is anyway).