Max. amount for visa on arrival?

Some countries get 90 days (tourist visa). Not many. If you are working you are illegal. You should get the proper visa to work in Malaysia.

Its all based on nationality and some have to apply for visa in advance before leaving country.

Consult the proper channels

http://www.imi.gov.my/index.php/en/main-services/visa

I am asking because a friend of mine is travelling SouthEast Asia, and she plans to enter Malaysia several times. It is not about a visa for work.

Depends on nationality

http://www.imi.gov.my/index.php/en/main-services/visa

EvaMarbach, Visa on Arrival facility is granted to those nationaility that require Visa to enter Malaysia i.e. India, Pakistan, etc. Over time, this facility has been reduced or revoked altogether.

Certain nationalities can enter Malaysia without Visa. With or without Visa, on entering, the immigration will stamp a Social Visit Pass for a specific duration in your passport to indicate permitted length of stay.

Can you share the nationality in question?

Generally, people of the Western countries are less likely to be questioned even with entering Malaysia multiple times. Africans and Asians are more prone to questioning when entering.

The thing that raises immigration officers attention is people who stay just under 90 days but then return after 1-3 days. Currently they may only give a short term entry on the second return. If this is a pattern it can be as short as 3 days. Genuine tourists are not usually affected, but will probably be questioned and perhaps asked for documentation. If similar patterns are noticed for nationalities that have other no-visa requirement durations, they will also be the subject of attention.

I recently went through KLIA 2 a couple of times and noticed changes in the level of attention and also a set up where the officers referred a lot of cases to a supervisor at hand, to decide on what should happen regarding entry and length of stamp in passport validity.