Having different launcher versions cannot cause MP problems, but should be fixed anyway. Current is 2021.8.1 . Please have her try this:
- exit the Steam app entirely
- uninstall Paradox Launcher v2 from the Windows "Apps and features" utility, if still present.
Delete the following folders if still present:
- C:/users/<UserName>/AppData/Local/Programs/Paradox Interactive/
- C:/users/<UserName>/AppData/Local/Paradox Interactive/
- C:/users/<UserName>/AppData/Roaming/Paradox Interactive/launcher-v2/
To see the AppData folder you'll need to enable View Hidden Items in File Explorer.
- run steam.exe as the Windows Admin user
- run the game from the PLAY button in Steam
IF that doesn't help, in this folder are some .log files:
C:/users/<UserName>/AppData/Local/Paradox Interactive/launcher-v2/
Please attach them here.
As for the MP issue first test with NO Mods at all enabled. If you can play MP then, both enable one mod, test again, enable another, test ... that way you can pin down which mod is the problem.
If you cannot play MP with NO mods enabled, check the game version and checksum in the MP lobby (NOT in the launcher). Anyone who does not see 3.1.1 (22a5) needs to do a full **clean** re-install:
- move any valued save games elsewhere, and user_empire_designs.txt from /Documents/Paradox Interactive/Stellaris/ if you have made any custom empires or races.
- "uninstall" in Steam-Stellaris
- manually delete both the Steam/SteamApps/common/Stellaris AND Documents/Paradox Interactive/Stellaris folders
- re-install game in Steam, run a Steam Verify when done.
- add stellaris.exe to the exceptions list of your antivirus app; ESPECIALLY if you have Windows Defender, add it to the Ransomware "Apps Allowed Through" list.
- start the game with no mods active and test
In particular you need to make sure there are no files or folders left under either the Steam Stellaris or Documents Stellaris locations, before installing again.