It is not a First Amendment issue at all. She is free to express any viewpoint she wants. If she wants a contract with Texas, she can still express any viewpoint she wants, but she must not participate in a boycott that Texas objects to. This is settled law back from the 1960’s. You can object to serving people of a particular race, but serve them you must if you open your doors for business. She is free to say she does not want to do business with Israelis, but if she wants to do business with Texas she cannot boycott them.
Strangely it is the BDS movement itself that tries to restrict what beverages students at a school can buy. BDS is an ideological opponent of individual freedom: it wants to dictate to Americans what they can buy and where they can travel. Now they whine about restrictions on their freedom. Great hypocrisy.