The average amount from SSI in Washington is around 600 dollars a month, but the maximum one can receive is 943 dollars monthly. Since Birdie has no monthly income, we'll assume she is receiving the highest amount.
The cost of living in Washington is pretty expensive, in the top ten of most expenisve states to live in. A one-bedroom apartment can range from 1000-1600 dollars a month (and we know that the apartment has just one bedroom since Synni is sleeping on the couch). That means Birdie would have to be paying at least 500-800+ dollars a month if we believe that she is paying for more than half. We don't even know if the rent counted for utilities, but let's be generous and say it did, leaving Birdie with around 400 to 100 dollars left.
Groceries is a little harder to figure out, but it averages to about 400 dollars a month per person. Granted we don't know what or how much these girls ate, and maybe when they went out to eat Synni paid the bill then. So, again, let's be generous and say Birdie is spending on average 200 dollars a month on groceries. This gives Birdie at most 200 dollars a month for any miscellaneous stuff.
I'm not sure how much Birdie originally had in her saving account before she moved in with Synni, but considering her age and previous spending habits, I can assume she had little to no money in there to begin with. Also interesting to note, she never mentioned anything in her Twitter post what she bought for herself; just for Synni. Not even the new touchscreen laptop, if we assume again, Birdie bought it for herself and Synni didn't help to pay for it at all.
