Lower gears is a good way to go......"she's still building strength" is probably the key phrase....

Remember some people (including me) are born spinners and would rather sit and let the gears help us up a hill..this might be true for her to......

She'll get stronger as well without the high gear mashing,and might be quite happy spinning next to you,while you jump out of the saddle

That being said,to stand,shift to a higher gear,stand on the downstroke and balance the downstrokes with your arms....it's going to feel different because the arms are in play

If she is interested she'll get it,but there are other ways