The context of the swimming gesture (I didn't remark the "difficulty" part in her gesture, even if that went into the official transcript) was not stopping boats, where the swimming gesture might be interpreted differently, but rather it was a discourse by the interior minister where he claimed that the RN voted for the regularization of 10,000 sans papiers. According to the minister that was roughly the same law "minus 15 symbolic measures" that RN had opposed earlier in the Senate. It was those remarks that prompted Le Pen's gesture. Somewhat more liberally, that could be translated the she meant the minister was "grasping at straws", given the context.
She also made a nap-time gesture shortly after that.
The minister launched in quite an acerbic tirade against Le Pen, saying in the end that all she had managed during her political career were "small coups" and that she was not "ready for power", followed by a political comparison with the far right of the 1940s only being willing to "surrender".
Whether that's fair criticism in this context... According to the New Enterprise, the law project did not in fact pass as proposed by the government, which would have granted automatic "papers" in some cases, but rather it was amended to make the granting of those dependent on a case-by-case decision by prefects.