HELP! URGENT! Work Permit for non EU married with EU citizen

Hi everyone! I need help to understand some issues with the work permit for non EU in Belgium.
I will explain briefly the situation.
I'm Italian and I moved in Belgium last October (2 months ago) with my girlfriend.
We are in a relationship since February ( almost 1 year ).
I'm working with a weekly contract that I sign every week, with the interim agency, but I'll work there for sure until June ( with possibility of extention ).
My girlfriend is Serbian ( non EU ), she is on a visa D that will expire in February / March, she is doing a traineeship at the EU commission,
We rented an apartment together and we are both on the lease with a regular contract of 1 year.
The problem is that her visa is gonna expire in March and then she will have to go back to Serbia.
We both put a lot of effort to come here and we would like to stay but apparently she can't.
I was considering to get married here in Belgium at the comune, my question is:
once you get married here with a non EU citizen who is already in the country with a temporary short visa, can she stay here in Belgium and get a work permit?
How long it would take once married to get a work permit?
There will be any issue if my contract is not a permanent or long term contract?
Please someone who has had the same issue can give me some tips?

Thanks

Sorry made many changes. Here is the final one:

She can work based on an approved residency card F. For her to convert from visa to residency, once you're marriage is done, she will first need to apply for her residency based on marriage to a EU national. That takes exactly 6 months, not a day less. Then before her visa expires, she can continue to stay based on an orange card given by the city hall. At this point Im not sure if she can work. In most orange card cases the applicant can work but find out in your case. Then once the 6 months are up and her F card application is approved she can then work for any employer with no need of a work permit.

For your contract I dont think that they are strict  about your contract type (unlike the application for spouse of Belgian citizen where you need a full time contract), so my guess is that your interim contract is ok, as long as it exists for the duration of the 6 months, so keep working.

She has already the residency! I mean I don't know if it's called residency but we went to the foreigners office to register ourself and our address, and they give us a national number.

A person can have residency based on many reasons. When her card arrives please post back what card type she has received. A card, F card whatever it is please inform.

i will, I think it should be a short term card though, since her visa expires in March

Hi Marcello, if you guys get married then she can stay.i know a Dutch girl that moved here to get married with her none eu boyfriend because it was too difficult in Holland. She stayed for 3 months working in a cafe then got married. The guy is still here so it worked. And he could work. The only thing is they ask for a lot of documents that needs to be legalised and that might take time!  so if I were you in would go to the city hall ASAP.

If you get married or a co-habitation visa she won't need the work permit seeing as she is in a relationship with a EU Citizen. I'm not married but Co-habitation and was told by my Commune that because I reside with a Citizen I don't need one... In any case ask your Commune. Once you announce for marriage then I'm guessing they would probably make a temporary residency. If you don't or don't get married,then they would deport...