What Are The Uses And Side Effects Of Clexane 40mg 0.4 Ml?

How long should my mother (72 years) be taking 40mg 0.4ml Clexane after hind foot fusion operation (was switched to this from oral drug because of slight incision weeping). Discharged today with one syringe, and told by hospital to take for next 3 months. I thought only recommended for 14 days max (been having it for about 6 days now out of 12 day stay in hospital). Returning to hospital this Friday for staples to be removed (Hamburg, Germany). Regards