Hi and welcome to HCM
Well, without a clinical evaluation it would be difficult to determine the cause of the lump. From description pain and swelling over her right thigh seems to be inflammatory in nature.
I advice her to give rest to the part affected, take anti-inflammatory drug like motrin
1 tablet with food as and when required (upto 4 tablets daily) to reduce pain and inflammation and consult your doctor for thorough examination of thigh and rule out any infective cause.
Hope this will helps you. Take care.