Can a French tourist who extends a visa-on-arrival in Thailand return after a short trip to Bali and receive another extension?

If a French tourist enters Thailand with a visa-on-arrival and extends that for thirty days, will she be able to do exactly the same thing after flying to Bali for two or three days?

In other words, can she spend four months in Thailand - minus a few days exactly in the middle of her trip - without worrying that she will not be readmitted to the country or that she will not be permitted to extend her visa after her short absence from Thailand?

I would be grateful for some reassurance from people who understand the system.