If the FTC were arguing that she misinterpreted "may" then yes. They would have to argue that these precedents should be rejected in the 9th circuit. This is an aweful argument. If you interpret "may" in this context to mean anything with any infintessimally tiny chance of occurring, rather than something with a reasonable probability of occurring, then literally any merger could be blocked. The law would then be arbitrary and capricious , and result in a procedural due process violation in that the FTC would have unchecked power to block any merger based solely on the vagueries of the future being unknown, which could render the Clayton Act unconstitutional. There needs to be some limitation beyond what is possible, in interpreting "may" in this context.

When interpreting statutes, there are rules of statutory construction. One of the basic ones is that, where more than one interpretation is possible, then where possible, you must interpret a statute in a manner that does not violate the constitution. The underlying premise is that we should not presume that Congress intended to pass a law that could not be enforced because it is unconstitutional. Another rule is that where possible, you do not interpret a phrase in such a way that it renders another portion of the statute meaningless. The phrase we are looking at here is: “where in any line of commerce or in any activity affecting commerce in any section of the country, the effect of such acquisition may be substantially to lessen competition, or to tend to create a monopoly.” 15 U.S.C. § 18. If we interpret "may" to mean "could in any possible future, no matter how unlikely" then it would apply to every merger. This would render the phrase "or tend to create a monopoly" completely ineffective and superfluous.

The FTC, if this was what they were arguing, would have one hell of a hill to climb, basically asking for the power to block any merger they want, but still somehow keep the law constitutional. When an agency tries to claim broad new powers that it has not previously claimed, our current Supreme Court likes to smack them down, using the "major questions" doctrine. Basically what that boils down to is that "you have never successfully asserted a particular power before, Congress never changed the law to more specifically give it to you, and such a broad and sweeping use of a 'newly discovered' power requires specific new authorization from congress." You can see an example of this line of reasoning in the recent case rejecting broad student loan forgiveness.

There would be REAL risk in doing this now, as the FTC, with this Supreme Court. This is a case with a weak factual badis for the FTC. Bad facts make bad law. If they assert this power in an appellate court they're likely to be definitively told they don't have it. More and more cases like that mean less and less openness to a judge even considering a more open version of "may".