Well, long story short, if she is weak and not strong she will probably be poor on bars; especially as she gets to higher levels.
Giants don't really take a lot of strength to do. Only the cast handstand straight or straddle to get high enough to bail and swing to giant. This can also be done with a free hip on high bar.
But most of her upper body strength work should be rope climbs and bar dips, either on a single rail or men's P-bars. If she can't do dips, she must learn to be able to do pushups with her elbows tucked into her sides first. I also like pseudo planche pushups where you lean forward planche-like and then do a pushup. I also like gymnasts to do some body rows instead of vertical pullup/rope work for horizontal pulling work.
Chin hold to candle is a common drill besides rope climbs for upper body/core strength. Pull up, rock back to cradle/candle and back to chin flex arm hang.
Iwannacoach is right in the sense that freehip and giants are very much "swing" skills.