Hi anna,
I am no means an expert on employment in Buenos Aires but as someone who is also looking for a part time gig I thought I would chime in.
1) The fact that you speak virtually no Castellano will be in many ways very limiting in your job search. BAs is not like Panama or Costa Rica where on average bilingual english locals are much more prevalent.
2) You speak english and are not Argentine....so at the same time you are an asset. Mostly to expat employers who have their own business, such as a restaurant or bar that caters to tourists. English is valuable and paying foreigners under the table are typically more attractive to foreign employers than paying Argentines--paying a severance package to Argentines is standard practice here, where as if they let you go they owe you nothing....and I'm assuming you have no work visa, which means you have no labor rights to protect you.
I know everyone does this and might be cliche but....have you considered getting certified and teaching english? With certification I'm sure you can get regular work....though you won't get rich and might have a problem supporting yourself with just that if you have no savings. Also try and look out for NGOs looking out for assistants. Also go to expat bars/restaurant....try and frequent one or two so they get to know you....then ask the manager about doing part time work or something like that. Lastly, from time to time there are listings of customer service jobs on here.
But if you're strapped for cash...I'm not sure my "tips" will help you much. Job hunting anywhere takes time...don't get disillusioned, don't give up.
I really should take my own advice...