If there was no legal marriage, only a 10 year commonlaw relationship, the husband owns a business but the woman's name is no where on the business, when the couple separates, does the woman have equal rights to the business, if so how can she prove they were together for that amount of time?

You must be certain about whether there was a common law marriage: 1) does law allow for it; and 2) did the parties fulfill the requirement under the law. As to the business, states have different laws pertaining to division of property; and whether a party is entitled to alimony. She can offer her own testimony as to the length of the relationship through pictures, tax returns, testimony of family and friends.

You can check into palimony
The palimony case is the latest in a string of such suits filed since
The term was coined in 1977 after actor Lee Marvin's companion, Michelle
Triola, won a landmark lawsuit. She argued that based on specific
Promises, a cohabitant can have property rights to the assets of another
Cohabitant.

One of the largest palimony awards was granted in 199exp4, when an
Orange County jury ordered Mag-Lite flashlight mogul Anthony Maglica to
Pay $84 million to Claire Maglica. The two never married but had lived
Together for more than 20 years and she had served as executive vice
President of the Ontario-based company.

As George said though common law, palimony and everything would be based on your states laws.

You don't say where your friend lives, which might have helped. Most US states have abolished common law marriage laws. If they split they both need lawyers to help straighten this out.

In general esp in the US there is no common law marriage except for a few states. Now if she an prove she added to the business, helped build it, she may have some claim, but it will be hard.