Hi Patt,
You may find the following threads very helpful to your question:
http://forum.portraitartist.com/show...ght=varnishing
http://forum.portraitartist.com/show...ght=varnishing
http://forum.portraitartist.com/show...ght=varnishing
http://forum.portraitartist.com/show...ght=varnishing
The truth I learnt about varnishing is that, unless your painting is most impasto, thin applications dry adequately within the month or so depending on humidity of your environment. So retouch varnish is possible.
So the ones you've done three months ago, should be OK if they're thin layered works of art. Explain to your customer the situation with those near completion - and ask if she'd want to wait for those to dry first, so you can complete your varnishing task on them. Or if she'd mind bringing them back and wait for herself, before hiring someone from her area to complete the varnishing process for her.
Either ways, presenting yourself this way assures your dedication to her job. Hope what I've said is useful to you.