She's right...加油does not have a specific translation...you have to go with your feeling on this one.
e.g. During a competition, if you in the crowd and cheering for your country:
Come on England! Come on England!
for a person:
Come on "person"
(只有男人可以说) Come on my son! << man to man
e.g. If you are telling someone to 加油 as they have a task to do:
Give it your best/try your best
You can do it
Give it your all
I know you can do it
Break a leg
Don't give up
Soldier on
Put your back in to it (only say this when they look like they are starting to get lazy!)
Put some elbow grease in to it (only say this when they look like they are starting to get lazy!)
Get in there!
And many many more that I can't think of right now!
REMEMBER, when you say these, you have to add some tone!!!! otherwise you sound stupid :-(
Men can add "my son" to pretty much ALL of these: "get in there my son!" "you can do it my son"
Don't ask why.....we just can :-) ladies cannot! hehe
for ladies a man can say "love" or "darling": "Get in there love" but not always
Hope that helps!