Strontium Copper Borate [SrCu2(BO3)2, or SCBO] features a two-dimensional orthogonal network of Cu dimers. It is known for its exactly solvable ground state consisting of singlet pairs. With its spin-1/2 magnetic moments arranged on this lattice, SCBO provides a realization of the Shastry-Sutherland model (SSM), where the full orbital bands are downfolded to an effective spin model with inter- and intra-dimer exchange interactions. The SSM is successfully used to study the ground state, phase transitions, and triplon excitations. However, capturing out-of-equilibrium phenomena, such as the coupling of electrons to light, requires a more comprehensive model. We derive such an extended effective model by performing ab initio DFT and Wannier calculations, projecting onto the relevant O p- and Cu d-orbitals. To reduce complexity, we construct one effective ligand orbital per Cu to substitute the physical O orbitals. This effective model provides the foundation for future simulations of pump-probe excitations, which will provide insights into charge-transfer phenomena in SCBO beyond the capabilities of the SSM.