Originally Posted by corporate-wage-slave

If you were to book a DUB-LHR-DUB service then you can be with her the whole way until the BLR gate check, and then return to DUB, so long as you get the timings right (and don't accidentally book an Aer Lingus flight!). You should read the passageway guide so you know how to go from (e.g.) T5B to T5A. You won't need to go via security again if you read the guide.

In which case, and knowing she may be in a wheelchair, you would have 2 routes, one via landside, and one airside. If you booked assistance you'd be going airside and you would be briefly separated since you would have to clear UK and Ireland passports - which is unnecessary hence why for you landside is easier. However you do it there is a security check, and however you do it there isn't a formal passport check for your mother.

For the flight from DUB-LHR you will arrive at gate 23 or near to there.