You are mixing your tenses. Better is She will be tired because she will have worked all day long. or She was tired because she worked all day long. or: because she had worked all day long.

There are a number of "correct" ways to express this cause-effect relationship (in addition to some mentioned above): "Having worked all day, she will surely be tired tonight." (very formal) "She's working all day, so I expect she'll be tired by tonight." "She's going to be tired from her long day at work today." "She's had a long day, so she's going to be wiped out." (most casual) Of course there are many more combinations, involving other structures and vocabulary. I just wanted to add some variety and texture.

"She felt tired because she has been working all day long."

that sounds like she will be tired (e.g.tomorrow) because she worked all day long (in past). by the way... all day long-gives a serious idea about Continuous, and if her condition comes directly from her work, why she will be tired in the future because of her past work? E.g. she works at a factory. every evening she comes home tired and nervous... just example as a result of everyday's hard work but in your case it depends on the context

I would say "She will be tired because she will have worked all day long" but I am not a native speaker.