The first time I did one all sort of strange stuff came out- like pale blobs- you don't get that in a regular enema!
What I would recommend is that if she is not doing enemas already, start with a few salt enemas (I think it's supposed to be a tsp per 500ml but not sure as nowadays I just fling a bunch of) salt in warm water) first, it's essential to get used to the feeling as coffee produces a much stronger reaction than salty water (for me). Start small (500ml to 1l) and slow and make sure the water is body temp (about 37c). Too hot/cold/salty/not salty/fast will just make you want to go immediately. Your body will get used to it over time (i.e. once a week for a few weeks) and gradually stop spasming and then you can work up to 2l enemas and start massaging your tummy. *Remember at the beginning not to plan anything after as you might need to go back to the loo- after a while you kinda know how long it takes for your body to process it.
At this point you're ready for the coffee! Follow instructions on the internet (I do mine wrong with boiled coffee- same amount you would put in per cup but rolling boiled for about 20 minutes then strained and salt as above but that's the way my body prefers it) and for me, it's better to do a salt enema first (or a day before), coffee (holding as long as possible!) and a small salt one afterwards to flush. I don't think you need to work your way up to coffee enemas but as I said the first time was really something and I would be petrified if I haven't been doing enemas for months before hand! A coffee enema is pretty much a whole day affair so leave plenty of time for it, eat gentle and clean and really just spend time to chill out.
You can get a bog standard enema bag from amazon or big pharmacies (there are special metal tins as well but they are well expensive.) and the coffee is supposed to be *special* by a brand called Wilsons (http://sawilsons.com/) but can get away in a pinch with organic. The salt should be sea or himalayan and ideally if you want to be perfect, warmed spring/ mineral water instead of tap.
Not so much in the UK, but there are a ton of one stop online shops selling coffee and the metal tin etc. in the US and Canada.
I like enemas but as they say, there are lots of pros and cons so it's a pretty personal (and icky subject). They do make me feel clean inside though!