I took some fabric with eyelet lace on one side and pleated it a bit at the and then sewed it in. In hindsight (after Mara has tried walking in the skirt) I should have gathered the fabric up even more as Mara with her really long legs doesn't necessarily take very dainty steps and she finds it tight. But the general concept works well.
Not every item of clothing that gets passed down to us fits the standard of modesty that we like but generally it isn't to hard to do a little modification. Having a little more covering always makes us feel more comfortable and happy so the little bit of time and effort is quite worth it.