Not exactly. They still could grind missions until the faction standing is up to 0 again, for example. To speed things up, Data Center missions or low-rung COSMOS-missions can help. Those agents need pure faction standing and won’t accept corp-standings, but on the other hand, they also accept modified faction standings.
If your friend’s modified Amarr standing is below 2.0, running Amarr-COSMOS will be a pain, since their lowest agents all demand 2+ standing. But you can avoid that again by using the many Caldari-COSMOS agents without any faction requirements for an easy boost, as Caldari-standings also raise Amarr-standings.
The Data Center agents can actually cost you standing if you manage to fail them, so make sure your friend has the needed tags already in their cargo before accepting and don’t talk to agents if your standing is too low. I’m not sure if their missions can expire and if they can, your friend would have to grind up to that standing and take the mission, or lose it forever.
To summarize, let your friend run a few easy Caldari-COSMOS missions and gift some pirate tags to the few available Amarr Data Center agents, that should be enough to boost faction standing above zero.
Here’s some links:
Hope this helps!