I am not a medical expert but my mother is going through the same thing. I have researched this subject over thousands of hours.
Klonopin is a benzodiazapine. Short term memory loss occurs with long term use,as does depression and anxiety. It is intended for short term use only (no more than four weeks).
Klonopin is likely to impair memory,(by reducing acetylcholine) cause depression (by reducing seratonin) and cause anxiety
Both Lexapro and Celexa are SSRIs, this effectively increases the availability of benzodiazapine, in addition to increasing seratonin levels.
The effect of Benzodiazapines in older people (over c 63) is effectively double that of a younger individual.
To put this in perspective, my mother was on a low dose benzodiazapine, however when we analysed levels in her blood these were EXTREMELY high, reducing the SSRI, reduced the amount of benzo.
I suspect that the benzo levels have been increasing over the last four years, causing memory loss.Now the Benzo levels are now "stable" your friend is experiencing withdrawal symptoms .
The Aricept will help increase apparent Acetylcholine levels thus assisting with memory / slowing the decline.
The earlier the withdrawal is started - the less painful it is. The longer withdrawal is postponed, the more likely there will be long term damage.
Withdrawal must be tapered, it may be that withdrawal of the SSRI (to remove the multiplying effect) is the first stage.
Unfortunately the side effects of withdrawal are multiple. Your friend must not suddenly stop taking the medications as the side effects will be unbearable.
It is possible that your friends symptoms will disappear once the medication is removed, and the side effects disappear
You may wish to look at these UK websites.
www.benzo.org.uk (In particular look at the Ashton Manual )