From the BBC, reporter Katya Adler accompanied Mariam and mother Saadiyia to a United Nations clinic.
Mariam is examined regularly here but the medicine she needs is often not available. Mariam's mother blames Israel's blockade, still in place on Gaza.
Most medicines are allowed into the territory, but their transfer can be slowed by Israeli and Palestinian bureaucracy, and the entry of medical equipment and other supplies is limited.
The World Health Organization says that at the end of November 2009, 125 of 480 essential drugs were at "zero level", meaning there was less than one month's stock left.
Israel says the military operation was - and the continuing blockade is - targeted at Hamas, not Gaza's civilians.
The Islamic movement has controlled Gaza since June 2007, and has launched thousands of rockets and mortars into Israel in recent years.
After weighing and measuring Mariam, Dr Salim Ramadan told us of the frustrations of being a doctor in Gaza.
He said Mariam's case was typical.
He often prescribes medicines to patients that either turn out not to be available in Gaza or that have been smuggled through tunnels under the border with Egypt, but at such a cost that few Gazans can pay.
Egypt also keeps its border with Gaza almost entirely closed.
"What to do?" he asked. "We have 65% of people living here under the poverty line and the situation is just getting worse."