Just posting to put a 'bug in your ear'.....I'm familiar with the 'deaf cat howling' syndrome, but I thought I'd mention this to you - something to consider/put-in-your-back-pocket-sort-of-thing - perhaps a consideration for her next annual checkup.
You haven't mentioned her age, but you did dementia - so, perhaps she is getting up there. Now, night howling in older cats is frequently enough associated with hyperthyroidism and hypertension. Here's a useful page from one of the absolute-all-time-best online resources - look at "Howling, Especially at Night": http://www.felinecrf.org/symptoms_tr...ts_index.htm#H
Certainly not to be disregarded.......