They are arriving on SU from SVO and they will have to go landslide first since they will have luggage to pick up (my mom won't though). I did check SU2300 and it looks like it *usually* lands early (not that this means much!)

So it sounds like she should go to Welcome Lounge, make use of it till it closes (I assume they will be able to tell her when/if their flight has landed yet) and then go upstairs to the Momento cafe and wait for her friends there?

One thought I had was to maybe book the Welcome service or guide service to meet them and take them to T1/Momento or Welcome Lounge, but I think it's my mom that's more likely to get lost if she has to go from Welcome lounge to Momento - the way you described it though, it seems like it should be quite easy (for most people ).