Well, according to my drug book, the doctor has her on the maximum dosage for Lexapro. It has a long half-life of 30 hours (stays in the body) and some of it's adverse affects (and other drugs just like it) are: palpitations, tachycardia, hypotension, dizzy, tremors, headaches, twitching, forgetfullness (Just what an AD patient needs), anxiety, nervousness, aggravated depression (sounds like your mother already and these are only *maybe* effects) nausea, diarrhoea, altered taste, fatigue,insomnia, decreased libido, rash AND vision disturbances.
*phew*
Lexapro is in the "Selective Serotonin reuptake inhibitor list, you might want to ask your doctor if any of the Monoamine Oxidase inhibitors might now be in order (next line of attack of depression) or the Tricyclic and other related antidepressants. Forwarned is forarmed ...
THAT being said, I have a few residents on anti-depressants. It took about 3 days to make a noticeable change and about 4 weeks for it to be fully working. My lady missed a couple of doses the other week and was bed-bound in misery until her "happy pills" came back into stock.
goodluck