I wish every HG woman had someone like you who not only cares enough to offer help, but who actually seek out an answer/advice on their own on this board.
I can tell you from my experience, that the texts and emails make a HUGE difference in keeping me from feeling lonely. Most days I feel so yucky, and can only handle texted-length communication. I know for myself that personal visits are too hard. I feel like I look awful, I stink, and it brings along the pressure to be "up" for whomever wants to see me. I know visitors have good intentions in making me feel better, but visits are stressful for me, and I always feel more pukey afterwards from talking, moving, getting dressed, etc.
What I usually need is for someone to be willing and available to just do the thing I need, without the need for much interaction. My in-laws drop by every wed evening. I know they're coming by, so I write out a list of what I need them to get from the grocery store. Maybe you can "tell" your friend that you can be by on any X day(s) and to have a list ready for what you can do to help (sweep/vaccumn, pick up meds/groceries, put in a load of laundry, etc.). Tell her that she can stay in bed, and you will just pick up the note from the kitchen table. I just give my credit card PIN to my inlaws along with my card to use, and I write others a cheque afterwards for any expenses.
This may sound like a really "unfriendly" way of going about things, but it may offer her the break she needs, and it will give you a non-intrusive but totally loving way to help her.
Just my 2 cents. Every HG person needs different things though, so it's always a tough one. You're a great person for thinking about even helping.
DD1 born Jan 29, 2010. Mod-Severe HG. Started treatment at 5 weeks. c-section (breech)
DD2 born July 23, 2012. Severe HG started treatment at 4 weeks until birth. VBAC!