Request a huge favour. The answer tells you all.
trust your instinct the first time as they probably are using you ,humans are survivalists ..i mean are you completely altruistic or are you using someone ...your not ?: ... really ?
WAKE up and smell the coffee ...your own coffee..you were right the first time..if your wrong..then SO WHAT..you were wrong big DEEEEAAAL.
Let your friend use you but only if it is 'use'ful for you !
If not then ditch the BEEATCH
try taking a step back n ask them to do something for you instead - see what happens
Easy. Ask her to do something for you that doesn't benefit her at all; if she balks, she's using you, and you will need to hold her at arm's length.
How does a best friend, or any friend for that matter, use you? The only thing I could think of is sex, but then I'm not so sure that is simply a friendship