Hi merriment, sorry to hear your dd is having problems settling at secondary school. It is nearly always a difficult transition to make if your dc has any kind of special need. My ds 13 has different diagnosis - primarily asd - but has had similar problems with making friends and feeling isolated.
The amount of help you can access via the senco will depend to some extent on what stage you dd is at on the sen register -school action action + or statement. Having said that having a high level of support from a 1 to 1 lsa throughout the school day isn't likely to help you make friends. but possibly being included in a social skills group run by the sen dept might help.
One possible means of support is the circle of friends where a pre-selected group of your daughters peers will be told in a simple way about your daughter's difficulties and appointed as her champions to look out for her. Link to some info on this here: www.inclusive-solutions.com/circlesoffriends.asp
This can also be done on a smaller scale via a buddy system, where your dd's form tutor can ask someone else from her class to stay with her at break-time and go with her to the canteen - this doesn't have to be the same person all the time and doesn't necessarily have to involve explaining about your dd's epilepsy and dyspraxia.
Informally you could see if your daughter would like to invite anyone from her class to come round to your house after school or to do something fun at the weekend. Making sure nice food/treats are available will help the process along.
Of course, a lot of these strategies are dependent on your daughter's wishes and sensitivities and how much she is willing to be upfront with others about the difficulties she faces and also on the sensitivity and emotional maturity of the other children involved. Hopefully by this stage in the year their form tutor should have a reasonable idea of personalities.
It is really worrying and I don't think there are easy answers but in your position I would contact both the senco and your dd's form tutor to discuss concerns and see what advice they can offer.