I've only read this stuff so correct me if i'm wrong, but she looks gravid to me ( full of eggs ) that thing protruding from her is her breeding tube so nothing to worry about
. Is she cleaning any specific area? if she is she will probably lay eggs there but they wont be fertile unless there is a male around.
You are correct
Only livebearing fishes (Guppies, Platies, Mollies, Swordtails, etc) can be pregnant and Angelfish are egg layers so the common term is "gravid".
To the OP, It's not unusual for single female Angels to lay eggs without a male but nothing will come of them without a male present and fertilizing them. They will be a good food source for any other fish you may have in the tank, however, she can also do some real damage to your other fish while trying to protect her eggs so you may want to remove whatever she spawns on and scrape those eggs off it and add them to your regular food. She will not be happy for a day or so but they usually get over it quickly.
If you see her with a another Angel in your tank, and that other Angel looks to be protecting her from any other fish you have in the tank, you may want to remove both these fish to another tank as they can be very protective of a spawning area and really go after the other fish in your tank.
Obviously, without knowing all the specifics of your set up, these are only suggestions as to what you can expect to see. Not all fish follow "the rules" but most do with these results.
If you are interested in breeding your Angels, there is a thread in the breeding forum titled " Wigglers at last!!!" which was an ongoing discussion by both professional and hobbyist Angelfish breeders all about breeding and raising Angelfish. Pretty much everything you need to know is in that thread.
Hope this helps