Its when Saturn is in the 7th that its advised that the astrologer will have difficulty reading chart accurately.
Saturn in the 1st gives negative answer in my expereince... So in your question you are worried about this girl, Saturn in 1st indicates that this will not come true, even though its causing you anguish over this, you do not have to worry about her, so to speak.
I would take Saturn to be this 'freind' as Capricorn is ruling his 11th house of friends. Her being in his 7th and retrograde could maybe mean that she is possibly someone from the past coming back (an ex girlfriend?)... her being in his 7th could mean that she possibly wants some sort of relationship with him.
But his ruler will oppose her. Although Jupiter (him) is strong in his own sign, he is also in Saturn's (her) term, he likes her. Funny Saturn is in Jupiter's detriment, she doesn't really seem to care much about him? Jupiter is also in your detriment. Something about him is making you feel unhappy and down.
Moon will trine Jupiter (him), sextile Sun (ruler of ur 12th house in his 3rd house) and then sextile Saturn (her). Could mean communication (hidden from you) between them. Of course it seems this has already happened as you discovered. But this is a future aspect here, so more of it will come. On the other hand because their rulers oppose each other, and the fact that Moon can't really bring their rulers together as Sun comes in between (translation of light is obstructed by Sun), it means nothing will come of it.
Last aspect of Moon to retrograde Saturn is not positive (Moon is also in detriment to Saturn), but it depends on what your question is. You were just asking who she is to him, that I already answered. She is someone who is interested in him, someone from his past coming back and he does like her or at least is accepting of her friendship. But in the long run, nothing will happen here, that opposition between their rulers tells us that there is separation and nothing much will come of it despite her intentions.
His ruler is approaching a conjunction to Uranus as well, so that could mean some sudden change for him, unexpected things happening.
hope this helps
R