Nearly 7 yo dd hates pants.
Maybe her underwear is too tight or itchy/uncomfortable. With the added discomfort of jeans/pants it probably really bothers her. Try a larger size. My DD outgrew her underwear recently and never said anything till they started to bother her. So finally I bought her a larger size and she has not had a problem since. (she only wears them part time since she still wears goodnites) But actually likes them better and thinks they are more comfortable) Hopefully she outgrows that SOON.
Yes, she's pretty much always been this way.