Let $G = N \rtimes K$ be a semidirect product (with $N$ normal in $G$). If $H < G$ satisfies $H\cap N = \{1\}$, must there exist a complement $M < G$ to $N$ such that $H < M$?
By a complement to $N$, I just mean a subgroup $M < G$ such that $M\cap N = \{1\}$ and $NM=G$.
Note that the projection $G\to G/N \cong K$ embeds $H$ as a subgroup of $K$, so $H$ is certainly isomorphic to a subgroup of a complement to $N$, but I'm asking for more.
I am particularly interested in the case where all complements to $N$ are conjugate to one another inside $G$.
No, not necessarily. There is a counterexample with $N = C_2$ and $K=C_4$ with trivial action of $K$ on $N$. So $G = N \times K$.
To get an example in which all complements are conjugate replace $K$ by a simple group, such as $A_5$. Then the complement is unique, but there are still diagonal elements of order $2$ that are not contained in that complement. In fact $K=A_4$ would also work.