Good questions, pepper! You are fortunate that it is your Mom! Trust is all in a joint account!
Being added as a jjoint account holder gives you jjoint ownership of the TL, but ALSO joint responsibility!
Lets presume, for a moment, to avoid saying anything to offend Mom (LOL!) that the joint account was held rather with Tony Soprano down at the Bing-a-Boom, or whatever his garbage company was called. I dont think the instant advantage would make you sleep as sound at night.
You become tied into the joint's credit.
I know, many will say, each person has his or her own credit report, and marriage, etc., does not meld your credit reports into a joint report. That is true. But take a moment and listen to the last webinar posted in the Credit Education tab above on this site. The point was made by no other than FairIsaac that, even though reports, and thus credit scores, are not merged, nonetheless potential lendors may pull the CR of others who are listed as joint accountants of yours when evaluatiing your risk, because you are legally obligated on those accounts.
There aint no free. Moms are probably pretty safe joint accountants. Spouses are in only about 50% of marriages. Hmmmmm.....